Method of waterproofing plaster



Patented Aug. 21, 1934 UN it D PTE FFEQ ii.

No Drawing. Application July 29, 1932, Serial No. 625,659

Claims.

In the preparation of a plaster of Paris object for electro-plating onone or all of its surfaces, it is necessary to render the objectwater-proof so that-it may be suspended in the plating bath 5 withoutinjury. This is commonly done by immersing the object in molten waxafterdrying. Occasionally the wax fails to penetrate certain areas of thesurface of the object, and the present invention deals with theelimination of this difficulty.

It is believed that in oven drying of the plaster, before waterproofing,soluble salts are brought to the surface thereof and crystallized,forming a coating which resists penetration by the wax.

The compounds in the plaster form the aforementioned salts on thesurface, and resist absorption of the wax.

According to the invention, an impervious formation of these salts isavoided by treating the surface of the plaster with an oily, greasy ornon-volatile fluid or dissolved wax before drying. The surface of theplaster is coated with a grease, wax solution, oil (mineral orvegetable), or a non-volatile material such as glycerine. It

is preferred to use a substance which is soluble in the water-proofingmaterial, such as mineral oil or petrolatum. The coating may be appliedby dipping, spraying or brushing.

A surface thus treated does not dry out rapidly,

and crystallization is thereby retarded. The usual tendency of thesurface to dry out while the interior is wet is avoided, and hence thereis no interruption of the evaporation stream. The oven may be heatedhigher than usual, with a rapid but gradual drying and without the sud:

den drying of the surface that would otherwise occur.

In a preferred embodiment of the invention,

hot molten petrolatum is used. This is not absorbed at once into thesurface of the plaster and remains longer on the surface during drying.

The invention is not limited to any of the materials specifically namedbut rather includes any non-volatile or slowly volatile material adaptedto penetrate the surface of plaster and prevent the impervious formationof salts therein or thereon.

Having thus fully described my invention, I claim:

1. In the drying of a plaster object preparatory to water-proofing, theoperation of treating the surface of the plaster, before drying, with amaterial adapted to prevent impervious crystallization of salts at saidsurface and subsequently subjecting said object to a drying operation,and finally impregnating said surface with a water-proofing materialafter drying.

2. In the drying of a plaster object preparatory to water-proofing, theoperation of treating the surface of the plaster, before drying, with anoily or a greasy material and subsequently subjecting said object to adrying operation, and finally impregnating said surface with awaterproofing material after drying.

3. In a water-proofing of plaster objects, the method consisting intreating the surface of the plaster object, before drying, with an oilyor greasy material, drying the object, and impregnating said surfacewith a water-proofing material in which the first material is soluble.

4. In the water-proofing of plaster objects, the method consisting intreating the surface of the plaster object, before drying, with an oilyor greasy material adapted to be absorbed in the plaster and lessvolatile than water, drying the object, and impregnating said surfacewith a

